Method of toughening manganese steel.



.UNITED STATES Patented June 23, 1903.

METHOD OF TOUGHENING MANGANESE STEEL.

SPECIFICATION forming part of Letters Patent N 0. 731,450, dated June 23, 1903 Application filed Deoemher 24, 1902. Serial No. 136,484.

To all whom it may concern.-

Be it known that I, ROBERT ABBOTT HAD- FIELD, asubject of the King of Great Britain, residing at Shefiield,county of YorlgEngland, have invented an Improvement in Methods of Toughening Manganese Steel, of which the following description is a specification.

My present invention has reference to improvements in the method of toughening manganese steel which forms the subject of my prior patent, No. 572,891.

As the result of costly and exhaustive experiments I have found that exceptional toughness and tenacity can be obtained by the following treatmentthat is to say, the manganese steel is put into a heating-furnace'the temperature of which is gradually raised, so that heat will be applied very gradually to the steel in order to prevent sudden expansion thereof, this preliminary heating being (as stated in the specification of my before-mentioned patent) conducted at a very slow rate, dependent upon the thickness of the steel, the thicker the steel the slower the rate of heating. Having been slowly heated to a temperature of from 750 to 800 centi grade, (seven hundred and fifty to eight hundred degrees centigrade,) the heating is forthwith expedited, so as to raise the steel as quickly as possible to the temperature at which itis to be plunged in cold water, which temperature, according to mypresentinvention, while varying within certain limits, dependent upon the character of the particular steel and the product required, is not less than 940 centigrade (nine hundred and forty degrees centigrade) or more than 1,125 (eleven hundred and twenty-five degrees centigrade,) preferably from 980 to 1,050 centigrade (nine hundred and eighty to one thousand and fifty degrees centigrade) in the case of castings and from 940 to 1,000 centigrade (nine hundred and forty to one thousand degrees centigrade) in the case of forged manganese steel.

I find that by treating manganese steel in the manner described the percentage of hardening carbon remaining in the toughened product varies according to the temperature to which the manganese steel wasraised previous to its being plunged into cold water, the higher the said temperature the less being the amount of hardening carbon present product. For example, by

in the finished (No specimens.)-

heating different manganese-steel castings, each composed of manganese steel of the same original composition, to 850 centigrade, (eight hundred and fifty degrees centigrade,) 900 centigrade, (nine hundred degrees centigrade,) and 1,000 centigrade, (one thousand degrees centigrade,) respectively, the amount of hardening carbon present in the toughened manganese steel was found to be .45 per cent., (decimal four five per cent.,) .36 per cent, (decimal three six per cent.,) and.32 per cent, (decimalthree two percent.) The less the amount of hardening carbon present in the finished product the tougher and less hard will be the product, andthe greater the amount of hardening product present the harder and less tough will be the product. Consequently it will be seen that by suitably and carefully regulating the temperature to which the manganese steel is raised-as, for example, by a pyrometerthe percentage of hardening carbon present in the finished product can also be regulated with considerable accuracy, with the result that toughened manganese steel of a more uniform character and reliable quality can be produced according to this invention than has heretofore been usual.

I claim- 1. The herein-described process of toughening manganese steel, which consists in slowly heating the steel to a temperature from about 750 to about 800 centigrade, and then raising the temperature rapidly to from 940 to 1,l25 centigrade, and finally plunging the highly-heated steel in cold water.

2. The herein-described process of toughening manganese steel by varying the amount of hardening carbon therein, which consists in slowly heating the steel to a temperature of at least 750 centigrade, and then quickly raising the temperature to at least 940 centigrade, increasing the temperature above said limits the tougher and less hard the desired product,and finally plunging the highlyheated steel in cold Water.

In testimony whereof I have signed my name to this specification in the presence of two subscribing witnesses.

ROBERT ABBOTT IIADFIELD.

WVitnesses:

BAIN L. CAMPBELL, EDWARD S. ALLsoP. 

